[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] x86/apic: fix disabling LVT0 in disconnect_bsp_APIC
On Fri, Jan 17, 2020 at 03:30:44PM +0000, Andrew Cooper wrote: > On 17/01/2020 15:09, Roger Pau Monne wrote: > > The Intel SDM states: > > > > "When an illegal vector value (0 to 15) is written to a LVT entry and > > the delivery mode is Fixed (bits 8-11 equal 0), the APIC may signal an > > illegal vector error, without regard to whether the mask bit is set or > > whether an interrupt is actually seen on the input." > > > > And that's exactly what's currently done in disconnect_bsp_APIC when > > virt_wire_setup is true and LVT LINT0 is being masked. By writing only > > APIC_LVT_MASKED Xen is actually setting the vector to 0 and the > > delivery mode to Fixed (0), and hence it triggers an APIC error even > > when the LVT entry is masked. > > > > This would usually manifest when Xen is being shut down, as that's > > where disconnect_bsp_APIC is called: > > > > (XEN) APIC error on CPU0: 40(00) > > > > Fix this by reusing the current LVT LINT0 value and just adding the > > mask bit to it. > > > > Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> > > --- > > xen/arch/x86/apic.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/xen/arch/x86/apic.c b/xen/arch/x86/apic.c > > index a6a7754d77..e4363639bd 100644 > > --- a/xen/arch/x86/apic.c > > +++ b/xen/arch/x86/apic.c > > @@ -281,7 +281,8 @@ void disconnect_bsp_APIC(int virt_wire_setup) > > } > > else { > > /* Disable LVT0 */ > > - apic_write(APIC_LVT0, APIC_LVT_MASKED); > > + value = apic_read(APIC_LVT0); > > + apic_write(APIC_LVT0, value | APIC_LVT_MASKED); > > } > > This really is ugly. It seems that we can't write LVT0 to the same > state that it has after reset/INIT. > > For the code however, both halves of the if() condition do a > read/modify/write. It would be nicer to have the read and write common, > with modify alone having the if(). As said on my reply to Jan, we could do the same as clear_local_APIC if that seems preferable. Thanks, Roger. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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